The present invention comprises a new and distinct variety of sweet cherry tree, botanically known as Prunus avium L., and referred to by the varietal name ‘Prim 31’. The new variety was discovered in Baden-Wuerttemberg, Germany as the result of planned breeding between cherry tree variety named ‘Sweet Early’ (female parent, unknown patent protection) and an unnamed and unpatented cherry tree variety as the male parent. The purpose of the breeding program was to produce high quality fruits with an early ripening time. The new variety was first asexually reproduced via cuttings in Baden-Wuerttemberg, Germany in 2006. The new variety has been trial and field tested and has been found to retain its distinctive characteristics and remain true to type through successive propagations. The present invention has not been evaluated under all possible environmental conditions. The phenotype may vary with variations in environment without a change in the genotype of the plant.
The new variety is similar to both parental varieties in exhibiting a medium early blooming time, but differs from its parental varieties in fruit ripening time, fruit firmness, and S-alleles. When compared to cherry tree variety named ‘PC 7144-7’, known and marketed as “Tieton” (U.S. Plant Pat. No. 8,051), ‘Prim 31’ has S-alleles/S1S4 and “Tieton” has S-alleles/S3S9, the fruit shape of ‘Prim 31’ is rounder than the fruit of “Tieton”, ‘Prim 31’ has a black-red fruit color and “Tieton” has a brown-black fruit color, ‘Prim 31’ exhibits a medium strong and wide tree habit versus the upright and strong tree habit of “Tieton”, ‘Prim 31’ has a fruit ripening time that is 5 days earlier than “Tieton”, and ‘Prim 31’ exhibits longer fruit stems and less fruit cracking than “Tieton”. When compared to cherry tree variety named ‘Prim 21’ (plant patent application Ser. No. 16/501,496), the varieties are similar in flowering time and fruit color, but the fruits of ‘Prim 31’ ripen later and are bigger than the fruits of ‘Prim 21’. Further, ‘Prim 31’ has S-alleles/S1S4 and ‘Prim 21’ has S-alleles/S3S9.